The invention relates to a liquid filter, in particular an oil or filter of an internal combustion engine.
A liquid filter of the aforementioned kind is known from DE 100 38 531 A1. This document shows a liquid filter, in particular for lubricating oil of an internal combustion engine, comprising a filter housing, a filter element, a support body and a slide valve, wherein the filter housing has a dirty liquid feed, a clean liquid outlet and a liquid drainage channel, wherein the filter housing has a housing body and a housing cover, which are connected to each other in a detachable and sealing manner, wherein the filter element is inserted into the housing in such a manner that a dirty side is sealingly separated from a clean side, wherein the filter element encloses an filter interior in which the support body is arranged, and wherein the liquid drainage channel is closed by the slide valve in an openable manner. It is important here that the slide valve is detachably connected to the support body or, alternatively, is connected to the cover via a connecting piece. The slide valve can have a centering region which is guided in the housing body. Here, the centering region can be guided in the housing body in such a manner that when replacing the filter, the slide valve is held by a clamping force, as a result of which a spring acting on the slide valve in the opening direction becomes dispensable.
It is regarded to be a disadvantage of this known liquid filter that in particular when manufacturing the centering region on the one hand, and the housing body part guiding said centering region, on the other, high accuracy with very tight tolerances is required so that these two parts can be moved relative to one another in any case with sufficiently high friction forces which are necessary for holding the slide valve in the open position, but, at the same time, not with friction forces which are too high and could cause a premature disconnection of the slide valve from the support body or the connecting piece. An additional difficulty is that over time, the centering region, which is constantly under tension, is subjected to relaxation and due to its friction in the housing body is subjected to wear, which influences the friction forces and, in particular, reduces the friction forces in the course of the operating time. Moreover, the O-ring seals used in this known liquid filter tend to adhere on the wall of the housing body, which makes it difficult to release the slide valve from its closed position, and which likewise can result in an unintentional premature disconnection of the slide valve from the support body or the connecting piece.